Abstarct: Abstract In recent decades, there has been a gradual increase in the construction of twin tunnels to address the demands of urban infrastructure in densely populated cities. The determination of the ideal distance between these tunnels and their interaction with one another during the tunneling process has emerged as a crucial concern. In the context of this study, the investigation of this particular issue has been undertaken in relation to Tunnel No. 9 of the Tehran-North Freeway. Tehran-North Freeway Tunnel No. 9 is situated within the vicinity of Karaj-Sulqan, spanning from kilometers 9 + 475 to 9 + 835 km. The geological formation of the tunnel primarily consists of sandstone, tuff, and siltstone, with a predominant presence of hard rock. Beyond a distance of 35 meters from the exit of tunnel portal number 9, bridge number 6 commences, necessitating the intersection of the left and right tunnels within the designated domain. Therefore, investigating the reduction of the distance between the two tunnels and their stability is of particular importance. For this purpose, five cross-sections with a length of 100 meters each (where the distance between the twin tunnels is reduced from 8.9 to 1 meter) were considered. Excavations were conducted in stages, first for the right tunnel and then for the left tunnel, using conventional methods. The diameter of the right tunnel is 14.76 meters, the diameter of the left tunnel is 12.79 meters, and the tunnels have a horseshoe-shaped geometry. In this research, numerical methods of finite element method (using Phase2 software) and finite difference methods (using FLAC3D software) were employed to investigate the interactions and the effect of reducing the distance between the tunnels. The load that causes the tunnels to collapse is mainly influenced by the depth of the tunnels and the column width between them. baxsed on the results of the sensitivity analysis, the reduction in the distance between the two tunnels and the decrease in overburden led to a reduction in displacement values.